Recent improvements in lighting technology have developed white solid-state lamp technology based on the use of ultraviolet and blue GaN/InGaN light-emitting diodes (LEDs). This technology offers the exciting potential of highly efficient low voltage lighting sources that are rugged, highly reliable, and inexpensive. For highly industrial countries, the potential energy savings are very significant. In the U.S., about 20% of all electricity and about 7.2% of all energy is used for lighting. Energy savings also can result in environmental improvements by lowering the emissions from coal or oil fired power plants. Low voltage solid-state lighting also offers the opportunity to take advantage of local power sources, reducing the need for expensive power grids. Low voltage solid-state lighting offers a wide range of new lighting sources and products, including distributed panel lighting, conformable lighting systems, and intelligent lighting schemes.
A white solid-state lamp can be obtained by coating a conventional diode with a phosphorescent material, such as coating LEDs of GaN/InGaN-based epitaxial structures with phosphor. The phosphor absorbs the diode emission of blue or UV light and re-emits a broad band of yellow-green or red and green light. The re-emitted light combines with the original unabsorbed blue light to produce a white light.
FIG. 1 shows a schematic diagram of a typical white light LED lamp. LED lamp 20 comprises a first lead frame 22 having a reflector cup 24, a second lead frame 26, an LED chip 28 disposed in the reflector cup 24 and electrically connected to the first lead frame 22 and the second lead frame 26, a phosphor epoxy coating 30 disposed in the reflector cup 24 about the LED chip 28, and an epoxy lens 32 molded about the first lead frame 22 and the second lead frame 26. Dispensing the phosphor epoxy coating 30 into the reflector cup 24 requires a separate manufacturing step, increasing the time and expense of production.
FIGS. 2A & 2B show schematic diagrams of a typical surface mount technology (SMT) white light LED lamps. FIG. 2A shows an SMT LED lamp manufactured by a pre-dip process. The LED chip 40 is disposed on and electrically connected to metal contact base 42 having a reflector cup 44. A phosphor epoxy coating 46 containing phosphor particles 48 fills the reflector cup 44 and covers the LED chip 40. An epoxy lens 50 is molded over the phosphor epoxy coating 46. Although the phosphor epoxy coating 46 is disposed close to the LED chip 40 for efficient light production and the epoxy lens 50 can be clear so as not to interfere with light transmission, variability of phosphor concentration and geometry in the phosphor epoxy coating 46 causes color and light transmission inconsistencies between different LED lamps. In addition, dispensing the phosphor epoxy coating 46 into the reflector cup 44 requires a separate manufacturing step, increasing the time and expense of production.
FIG. 2B, in which like elements share like reference numbers with FIG. 2A, shows an SMT LED lamp manufactured by a pre-mix process. Phosphor epoxy lens 52 containing phosphor particles 48 fills the reflector cup 44, covers the LED chip 40, and forms an optical dome 54. Although the large volume of the optical dome 54 produces consistent color and no extra manufacturing step is required to fill the reflector cup 44, the disposition of the phosphor particles 48 throughout the whole phosphor epoxy lens 52 interferes with the light transmission, making the LED lamp inefficient.
It would be desirable to have a method for selectively depositing light emitting film on a light emitting base layer that would overcome the above disadvantages.